The present invention relates to wireless terminals and a wireless communication system in wireless communication which selects a communication channel.
With the widespread use of wireless communication devices, the problem of electric wave interference between the devices has been appearing. As means for circumventing the wave interference, it is possible to measure the states of use of usable wireless channels and use the wireless channels which do not interface with each other.
As disclosed in U.S. Pat. Application Publication No. US 2002/0060995 A1, a conventional method for selecting a communication channel in wireless communication measures the states of use of wireless channels at each of a base station and one or more wireless terminals. The wireless terminal notifies the base station of the results of measurement, while the base station is define as means for analyzing the measurement results and indicating the communication channel to be used for communication to the wireless terminal.
However, the prior art technology mentioned above has not described a specific method for analyzing the measurement results at the base station. When the method of analysis used at the base station is merely a method for determining the communication channel by immediately analyzing the measurement results upon each receipt of the measurement results from any wireless communication terminal, the determined communication channel may possibly be a channel with conditions preferred only by the wireless terminal that has first transmitted the measurement result notification. For example, there is the possibility that, with the communication channel newly selected by the base station, the wireless terminal which has performed important data communication may be affected by wave interference and the data communication may be inhibited thereby.
As a specific example, a wireless network structure composed of three wireless terminals is shown in FIG. 1. The wireless terminal A is assumed to specify one of a plurality of wireless channels usable for communication between itself and each of the other wireless terminals B and C as the communication channel to be used for actual communication and perform data communication.
Each of the wireless terminal A and the other wireless terminals B and C has the function of measuring the respective states of use of the plurality of usable communication channels. Each of the wireless terminals B and C transmits the measurement results as a measurement result notification 104 to the wireless terminal A. The wireless terminal A is assumed to have the function of individually analyzing the contents of the measurement results received from the wireless terminals B and C and issuing, when there is a channel in a state more optimal than that of the current communication channel, a channel change instruction 105 for changing the communication channel to each of the wireless terminals B and C.
FIG. 2 is a table showing the results of channel measurement transmitted from the wireless terminals B and C to the wireless terminal A. The table of FIG. 2 shows evaluation values obtained as the results of measuring the channels ch1 to ch4 at each of the wireless terminals A, B, and C. In the table of FIG. 2, larger values represent lower evaluation levels. For example, when the wireless terminal A is first notified of the measurement results from the wireless terminal C and the channel ch4 is currently used as the communication channel, the channel ch4 has the value of 10 as the measurement result indicating the least optimal communication state in the table. Accordingly, the wireless terminal A selects the channel ch1 with the value of 0 as the most optimal channel and issues the channel change instruction to each of the other wireless terminals B and C in the wireless network such that the communication channel is changed from the channel ch4 to the channel ch1. At this time, if it is assumed that the wireless terminals A and B are currently performing important data communication therebetween and the wireless terminal C is performing no data communication, the problem occurs that the changing of the communication channel from the channel ch4 to the channel ch1 based on the measurement results from the wireless terminal C causes trouble in the data communication between the wireless terminals A and B that has been optimal thus far. In the table of FIG. 2, each of the results of measuring the channel ch1 at the wireless terminals A and B has the value of 2 so that, from the comparison with the value of 0 of the channel ch4 before the channel change, the communication state has deteriorated. Thus, the changing of the communication channel based only on the results of individual measurement at any of the wireless terminals may occasionally cause trouble in the communication of another wireless terminal.